The present invention relates to an air compressor, and more particularly to the bearing structure of the air compressor in which a rotary shaft extending from both sides of a compressor rotor is supported by bearings provided on a front side and a rear side of the compressor.
Generally, in a rotary compressor, i.e. in a compressor in which the volume of the internal cylinder is changed by a rotor, a rotor having slidable vanes is rotatably housed in a cylinder chamber comprised of a cylinder, a front block and a rear block attached to both ends of the cylinder, and the cylinder chamber is divided into a plurality of smaller chambers by the rotor vanes. The desired compression is carried out in the cylinder chamber by rotating the rotor at the desired speed of rotation.
A dynamic pressure bearing has already been developed for use as the bearing for rotatably supporting the rotary shaft extending from both sides of the rotor. When a refrigerant gas absorbed from an absorbing port at a low temperature and a low pressure is passed through the passage of the front block, the temperature of the bearing portion of the rotor becomes low, but the refrigerant gas once compressed has a high temperature and a high pressure, and the cylinder chamber is at a high temperature.
As a consequence, the temperature of the bearing portion of the front block near an inlet becomes low and the front block bearing portion shrinks because of thermal contraction, while the bearing portion near the cylinder chamber is at a high temperature and expands because of thermal expansion. Therefore, the clearance becomes larger than the normal slit S at the bearing portion A and the clearance becomes smaller than the normal slit S at the bearing portion B as shown in FIG. 1. As a result the problem of locking often occurs between a rotary shaft 7A of the rotor and the bearing portion near the inlet. Furthermore, when the electromagnetic clutch for transmitting rotation from an engine to the compressor shaft by way of a pulley is attached to the compressor body, if the center of the electromagnetic clutch shifts from the center of the rotary shaft by a distance C, the rotary shaft whirls with an eccentric motion relative to the center of the electromagnetic clutch, whereby the problem of locking between the rotary shaft and the bearing portion occurs.